1. Field of the Invention
The present invention relates to a knock detection apparatus for an internal combustion engine for detecting knock that occurs in the internal combustion engine.
2. Description of the Related Art
Ions are known to occur during fuel combustion in an internal combustion engine. When probes applied with a high voltage are provided in a cylinder of the engine, such ions are observable in the form of an ion current. In addition, a vibration component of a vibration frequency identical to that of the knock is known to be superposed onto the ion current, and the vibration component is extracted to perform knock control.
With a conventional knock control apparatus for an internal combustion engine, an ion current as described above is measured in such a manner that a high voltage is generated to observe the ion current by using a secondary voltage generated by an ignition coil, and the high voltage is applied to ignition plug terminals following the termination of discharge for ignition. The vibration component of the knock frequency band is extracted from the ion current by using a bandpass filter (BPF). Then, the extracted component is amplified (signal amplification) by an amplifier, the signal is compared with a detection threshold value, and the waveform thereof is shaped according to the comparison. As a result, knock pulses are generated. Subsequently, the knock pulses are sent to an engine control unit (ECU), and a determination is performed as to whether knock has occurred. According to the determination result, ignition timing is controlled. That is, knock control is performed (refer to, for example, Patent Document 1).
Patent Document 1
JP 10-9108 A (FIG. 6)
However, depending on the operation condition of the internal combustion engine, even when knock is not occurring, a case may occur in which a vibration component identical to the knock frequency is superposed on the ion current.
A knock detection apparatus such as a bandpass filter which is designed to extract a knock vibration component is incapable of detecting the difference between knock and the above-described noise having the same frequency component as a knock frequency. In addition, many difficulties are present to extract only a knock signal from the noise that is equivalent in both vibration amplitude intensity and vibration duration to noise that involves knock of a high magnitude. These difficulties have introduced significant problems in the development of knock detection apparatuses, particularly, of the type employing an ion-current detection method.
The present invention has been made to solve the problems described above, and an object of the present invention is therefore to obtain a knock detection apparatus for an internal combustion engine which is capable of accurately distinguishing knock from noise even when noise with a frequency component identical to a knock frequency component is superposed on an ion current signal.
According to the present invention, a knock detection apparatus for an internal combustion engine includes an ion-current detection device, a knock detection device, a center-of-gravity calculation device, and a knock determination device. The ion-current detection device applies a voltage to electrodes provided in a co-combustion chamber of the internal combustion engine, and detects an ion current flowing between the electrodes via ions generated following combustion in the combustion chamber. The knock detection device detects knock occurring following an abnormal rise in either pressure or temperature in the combustion chamber of the internal combustion engine. The center-of-gravity calculation device calculates a gravity position of an ion current waveform detected by the ion-current detection device. Further, the knock determination device determines knock or noise in accordance with outputs of the knock detection device and the center-of-gravity calculation device.